Precision Wide Range (3 nA to 3 mA)

High-Side Current Mirror

ADL5315

Rev. 0

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FEATURES

Accurately mirrors input current (1:1 ratio) over 6 decades

Linearity 1% from 3 nA to 3 mA

Stable mirror input voltage

Voltage held 1 V below supply using internal reference

or can be set externally

Adjustable input current limit

2.7 V to 8 V single-supply operation

Miniature 8-lead LFCSP (2 mm × 3 mm)

APPLICATIONS

Optical power monitoring from a single photodiode

General voltage biasing with precision current monitoring

Voltage-to-current conversion

FUNCTIONAL BLOCK DIAGRAM

VOLTAGE

REFERENCE

CURRENT

LIMITING

COMM

VSET

NC

INPT

CURRENT

MIRROR

1:1

ADL5315

4

2

7

SREF

3

1

6

VPOS

20k

Ω

5

RLIM

8

IOUT

Figure 1.

GENERAL DESCRIPTION

The ADL5315 is a wide input current range, precision high-side

current mirror featuring a stable and user-adjustable input

voltage. It is optimized for use with PIN photodiodes, but its

flexibility and wide operating range make it suitable for a broad

array of additional applications. Over the 3 nA to 3 mA range,

the current sourced from the INPT pin is accurately mirrored

with a 1:1 ratio and sourced from the IOUT output pin. In a

typical photodiode application, the output drives a current-

input logarithmic amplifier to produce a linear-in-dB output

representing the optical power incident upon the photodiode.

For linear voltage output, a single resistor to ground is all that is

required. The photodiode anode can be connected to a high

speed transimpedance amplifier for the extraction of the data

stream. The voltage at the INPT pin is temperature stable with

respect to the voltage at the VSET input pin, which it tracks. A

temperature stable reference voltage is provided at the SREF

pin, which, when tied to VSET, fixes the voltage at INPT 1.0 V

below VPOS. VSET can also be driven from an external source.

The VSET input has very low input current and can be driven

as low as the bottom rail, facilitating nonloading voltage-to-

current conversion as well as minimizing dark current in

photodiode applications.

The ADL5315 also features adjustable input current limiting

using an external resistor from RLIM to VPOS. The maximum

current sourced by INPT (and IOUT) can be set between 1 mA

and 16 mA, beyond which the voltage at INPT falls rapidly

from its setpoint. Connecting RLIM directly to VPOS provides

basic input short-circuit protection with the default current

limit of 16 mA typical.

The ADL5315 is available in a 2 mm × 3 mm, 8-lead LFCSP and

is specified for operation from −40°C to +85°C.